In the early days of personal computers ("PC"s), microprocessor central processing units ("CPU"s) and other major electronic components thereof were soldered directly to a circuit board. Although this was a cost-efficient mounting method as far as manufacturing was concerned, there were several major drawbacks. First, heat generated during the soldering process sometimes overheated the components, rendering them useless or limiting their lifetime. Although soldering techniques improved over the years, such overheating remained a concern. Second, if the component was found faulty during a later-performed test, the component had to be unsoldered from the circuit board and a new one resoldered in its place, again with the risk of heat overexposure during soldering. As the components grew more integrated and sophisticated, pin count increased, increasing heat delivered to the component during soldering and greatly complicating component replacement.
Because of the above-discussed deficiencies of direct solder-mounting of components, low insertion force ("LIF") sockets were developed. LIF sockets were designed to be directly soldered to the circuit board in lieu of a component. LIF sockets provided a plurality of apertures on an upper surface thereof for receiving the component pins. Each of the apertures contained a spring-loaded contact that frictionally gripped each pin as it was inserted. The combined frictional force of all of the spring-loaded contacts on the component pins retained the component in the socket and provided for good electrical contact between the component pins and those on the LIF socket.
As component size and pin count continued to grow, however, LIF sockets became problematical. Each spring-loaded contact in the LIF socket required a certain amount of spring force to maintain good electrical contact. However, as pin count grew, the total spring and frictional force also grew. At some point, the combined frictional force of all of the spring-loaded contacts made insertion or extraction of the component from the LIF socket difficult. Sometimes, the required insertion force bent or folded slightly misaligned component pins, placing the entire component at risk. If the insertion or extraction force was not applied uniformly, pins were at risk of being bent or broken. The design of many-apertured LIF sockets required keeping individual aperture friction to a minimum to keep total insertion or extraction force to a practical level. However, a sufficient amount of spring-loading in each aperture was needed to maintain reliable electrical contact. Often, a special-purpose component removal tool was required for extracting many-pinned components (particularly microprocessor CPUs) from LIF sockets.
Today's PCs are often designed to operate with improved components as they are developed. For example, as an improved microprocessor becomes available, a user wishing to increase PC performance need only replace the existing microprocessor with an upgraded model. Unfortunately, many users lack the dexterity, gentility, strength and confidence necessary to install many-pinned components in LIF sockets. Thus, the many users that would benefit from the increased performance of a component upgrade are deterred from undergoing the transition.
In response to the user's concern, PCs are beginning to be equipped with zero insertion force ("ZIF") sockets to eliminate a need for the user to apply substantial insertion or extraction forces to upgrade components. Like LIF sockets, ZIF sockets are designed to be directly soldered to the circuit board. ZIF sockets also provide a plurality of apertures on an upper surface thereof for receiving the component pins. Unlike LIF sockets, the apertures do not contain spring-loaded contacts, but accept each component pin without substantial frictional resistance. An arm is rotatably mounted to the ZIF socket. Rotation of the arm causes a relative translation of portions of the ZIF socket with respect to each other. The portions place the component pins in a mechanical shear or bind within the apertures. The mechanical bind brings about a good electrical contact for each of the component pins. The combined mechanical bind of all of the apertures presents a substantial retention force to hold the component in the ZIF socket. Unlike LIF sockets, ZIF sockets do not need to sacrifice individual aperture retention force and concomitant electrical contact integrity to keep total insertion or extraction forces to an acceptable level. Thus ZIF sockets therefore typically have high retention forces relative to LIF sockets.
As components have increased in size and power density, it has become attractive to pair the larger components, particularly the microprocessor CPU, with a heat sink. Typically, this is done by providing a retention clip that wraps around the heat sink and grasps the component on its underside. The component and the heat sink therefore become a single assembly that can be inserted or extracted from a LIF or ZIF socket in a single step. Unfortunately, heat sink/component assemblies are relatively heavy. This becomes most disadvantageous when the PC is transported. As the PC is rotated, bumped and jarred, the weight of the heat sink/component assembly generates forces sufficient to dislodge the assembly from its socket. If forces are of sufficient strength, even components that do not have a heat sink attached may generate enough force to become dislodged from a ZIF socket.
Accordingly, what is needed in the art is a structure for providing additional component retention forces in a ZIF socket to minimize a probability of component movement or detachment while locked in the socket.